Testing hot water heater elements


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Old 05-11-10, 11:11 AM
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Testing hot water heater elements

I been living in the new house for about a year, the hot water never lasts(only for about 10 to 15 minutes). So I decided to change the elements. Turned the power off going to the hot water heater, drained the hot water heater, removed the elements. The elements were black, and one of them was covered in sediment. So I went to the local hardware store and got replacements (only $15.00 each!!) Installed them, turned water back on, & purged the lines. My question is when I tested the elements, one was 12.9 ohms, the other was 12.5 ohms. Could one be bad, because we have hot water for about 10 minutes? Also checked for a ground on both elements, nothing.
 
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Old 05-11-10, 06:54 PM
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13 ohm is the normal reading for a 4500 watt element..give or take an ohm or 2. Did you check the flow between the two screw connectors of the elements: If there is a positive reading, then the circuit is "closed" and the element is fine; if there is no reading, the circuit is "open" and a new element is needed. Also, if you get a reading on your meter between either of the screw connections and the metal element, the element is shorted and must be replaced.
Also I hope you flushed the sediment out of the tank before you started it back to heating. Sediment is the big killer for the bottom element as it has to heat the sediment before the water gets hot. You should flush the tank at least yearly by attatching a hose to the petcock valve at the bottom of the tank. Open the valve and let the water run until it comes out clear. You may need to turn the incoming water off and open the valve to see if it will run water out. It may be plugged up from never being flushed. You would need to run a thin wire into the open valve to try clearing the clog. Then attatch the hose and turn the incoming water back on to allow the pressure to flush the tank.
 
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Old 05-12-10, 03:42 PM
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Unless you had a more sophisticated, 4 lead, resistance tester, then just your test leads and contact resistance will easily give you plus or minus an ohm, so you have no problem with those items.
 
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Old 05-13-10, 06:29 PM
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the hot water never lasts(only for about 10 to 15 minutes).
It sounds as if the bottom element, which heats the bulk of the water in the tank, isn't operating. Assuming the element is good, you could have a thermostat problem, either top or bottom thermostat could be culprit. At what temperature were the thermostats set? The top element does the quick recovery and initial heating in the tank and then, when the top stat is satisfied, the top stat switches the power on one leg to the bottom stat. The bottom stat adds that one leg to the element only when the actual water temperature is below the setting on the bottom stat. The other leg should be hot to the bottom element at all times. I prefer both elements to be set at about 120 degrees.

With new elements, do you have any more hot water? How many gallons is the tank?
 
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Old 05-19-10, 05:06 PM
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10 or 15 minutes of hot water (depending on where you're measuring it at) could be a lower element not coming on, or it could be a bad dip tube, or, if you're able to run 3 gallons a minute or more through the valve where you're measuring (or timing) it at, that would be normal.

Given the resistance reading of about 13 ohms of the lower element, it's fine. But either of the thermostats could be faulty and not turning it on. (From a dead cold WH, the upper 'stat sends the power to the upper element only. Once that has heated to the temp. set on the 'stat, the upper 'stat then directs power to the lower element through the lower 'stat.)

A dip tube that has cracked or broken off is not directing the cold water all the way to the bottom of the tank as you use the water. If it is dumping the water off at the center of the tank you'll only have about 20 usable gallons of hot water (in a 40 gal. WH) before the cold water starts coming out of the hot nipple.

If you are measuring the flow at the tub spout (which has no restriction in it), it's very possible to drain a 40 gal. WH in 10 minutes or less.
 
 

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